Postman Pre-Request script to get access token for Twitch OAuth2

twitch-helix-oauth2-postman-prerequest.js

/*
 * Twitch Helix OAuth2 Postman Pre-Request Script
 * @see https://dev.twitch.tv/docs/authentication#registration
 * @see https://learning.postman.com/docs/writing-scripts/pre-request-scripts/
 */

const authUrl      = 'https://id.twitch.tv/oauth2/token';
const clientId     = pm.collectionVariables.get('clientId');
const clientSecret = pm.collectionVariables.get('clientSecret');

const qs = {
  'client_id': clientId,
  'client_secret': clientSecret,
  'grant_type': 'client_credentials',
  'scope': ''
};

function param(object) {
  let parameters = [];
  for (var property in object) {
    if (object.hasOwnProperty(property)) {
      parameters.push(encodeURI(property + '=' + object[property]));
    }
  }
  return parameters.join('&');
}

const getTokenRequest = {
  method: 'POST',
  url: `${authUrl}?${param(qs)}`,
  header: 'Content-Type:application/json'
};

pm.sendRequest(getTokenRequest, (err, response) => {
  const jsonResponse = response.json();
  const newAccessToken = jsonResponse.access_token;
  pm.collectionVariables.set('access_token', newAccessToken);
});